A typical electrolyte for electrolytic capacitors which has been hitherto used is an electrolyte of an ionogen dissolved in ethylene glycol. However, this type of electrolyte has a low specific conductance and tends to cause an impedance characteristic to deteriorate. To avoid this, usual practice is to add water to the electrolyte, but such an electrolyte is elevated in vapor pressure at high temperatures and is apt to react with an aluminum electrode, thus being unsuitable for use in a high temperature range.
In order to improve the above drawbacks, there have been proposed an electrolyte using .UPSILON.-butyrolactone as a solvent and a triethylamine salt of phthalic acid as described in Japanese Laid-open Patent Application No. 61-70711 and an electrolyte an amine salt of maleic acid dissolved in a mixed solvent of .UPSILON.-butyrolactone and ethylene glycol as described in Japanese Laid-open Patent Application No. 54-7564.
Moreover, Japanese Laid-open Patent Application No. 59-78522 describes electrolytes using quaternary ammonium salts of linear dicarboxylic acids, and Japanese Laid-open Patent Application No. 61-93610 teaches electrolytes using tetralkyl ammonium salts of 1,10-decanedicarboxylic acid or 1,6-decanedicarboxylic acid.
However, the known electrolytes comprising triethylamine salts of phthalic acid or maleic acid dissolved in a .UPSILON.-butyrolactone solvent are disadvantageous in that the acid dissociation is caused by the proton equilibrium of the triethylamine, so that ions are produced only in small amounts. Thus, a sufficiently high specific conductance cannot be obtained. On the other hand, with electrolytes using the quaternary ammonium salts of linear dicarboxylic acids or the tetraalkyl ammonium salts of 1,10-decanedicarboxylic acid or 1,6-decanedicarboxylic acid, the specific conductance becomes low because of the rather inappropriate combination with the acid. Accordingly, electrolytic capacitors using these electrolytes cannot disadvantageously lower the impedance characteristic.